Electrophotographic plate comprising a conductive substrate and a photosensitive layer containing an organic photoconductor layer composed of a hydrazone compound

ABSTRACT

An electrophotographic plate comprising a conductive substrate and a photosensitive layer containing an organic photoconductor layer composed of a hydrazone compound represented by the general formula (I): ##STR1## (wherein R 1  and R 2  are an alkyl, aralkyl or aryl group which may or may not have a substituent, n is a number of 1 or 2, and A is an aromatic hydrocarbyl group or aromatic heterocyclic group which may or may not have a substituent) and a binder.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

This invention relates to an electrophotographic plate, and moreparticularly to a high-sensitivity electrophotographic plate having aphotosensitive layer containing an organic photoconductive material.

(2) Description of the Prior Art

Heretofore, inorganic photoconductive materials such as selenium,cadmium sulfide and zinc oxide have been popularly used for thephotosensitive layer of the electrophotographic plates. Studies on useof organic photoconductive materials for the photosensitive layer of theelectrophotographic plates have advanced rapidly in recent years, andsome of such studies have materialized into practical use. The organicphotocondutive materials have many advantages over the inorganic ones,for example the former is light in weight and easy to fabricate as afilm and can also be easily manufactured into a sensitive plate, even atransparent sensitive plate in the case of using certain kinds of suchorganic materials.

Many studies have been made on the photoconductive polymers includingpolyvinylcarbazole, but these polymers are not always satisfactory incertain respects such as film-forming properties, flexibility andadhesiveness, and when these polymers are formed into a thin film, suchfilm tends to develop cracks or separate from the substrate. Additivessuch as plasticizer, binder, etc., are added to eliminate said defects,but addition of such additives gives rise to additional problems such asreduced sensitivity and increased residual potential. Thus, it was verydifficult to obtain a practical sensitive plate comprising organicphotoconductive materials.

On the other hand, the low-molecular organic photoconductive compoundsallow easy production of a sensitive plate with excellent mechanicalproperties because such compounds permit selection of a polymer withexcellent film-forming properties, flexibility, adhesiveness and otherproperties as binder, but it was difficult to find out a compound suitedfor making a high-sensitivity plate.

In view of the above, the present inventors have pursued furtherresearch into the organic low-molecular photoconductive compoundscapable of providing a high-sensitivity, and high-durability ofelectrophotographic plate and, as a result, found that certain specifiedhydrazone compounds are best suited for the purpose envisaged. Thisinvention was reached on the basis of such finding.

SUMMARY OF THE INVENTION

An object of this invention is to provide an electrophotographic platewith extremely high sensitivity.

Another object of this invention is to provide an electrophotographicplate with minimized residual potential which may cause backgrounddeposition of toner.

Still another object of this invention is to provide anelectrophotographic plate which is limited in variations of surfacepotential or sensitivity and accumulation of residual potentialresulting from repeated uses.

A further object of this invention is to provide an electrophotograhicplate with excellent durability.

The present invention, as taken in the broadest sense thereof, isintended to provide an electrophotographic plate characterized by havingan electroconductive substrate and a photosensitive layer containing anorganic photoconductor layer composed of a hydrazone compoundrepresented by the general formula (I): ##STR2## (wherein R¹ and R² arean alkyl, aralkyl or aryl group which may or may not have a substituent,n is a number of 1 or 2, and A is an aromatic hydrocarbyl group oraromatic heterocyclic group which may or may not have a substituent) anda binder.

DETAILED DESCRIPTION OF THE INVENTION

The photosensitive layer of the electrophotographic plate according tothis invention has at least one organic photoconductor layer containinga binder and a hydrazone compound represented by the general formula(I): ##STR3##

In the above formula (I), R¹ and R² represent an alkyl group such asmethyl group, ethyl group, straight-chain or branched propyl group,butyl group, pentyl group, hexyl group, etc.; an aralkyl group such asbenzyl group, phenethyl group, cinnamyl group, benzhydryl group,naphthylmethyl group, etc.; or an aryl group such as phenyl group,naphthyl group, anthryl group, pyrenyl group, acenaphthenyl group,fluorenyl group, etc. Most preferred among them is an aryl group,particularly a phenyl group. Said alkyl, aralkyl or aryl group may ormay not have a substituent such as, for example, an alkyl group such asmethyl group or ethyl group, a halogen atoms such as chlorine atom orbromine atom, an alkoxy group such as methoxy group or ethoxy group, anaryloxy group such as phenoxy group, an amino group such asdimethylamino group or diethylamino group, and an alkylthio group suchas methylthio group or ethylthio group.

Also in the above general formula (I), A represents a mono- or divalentaromatic hydrocarbyl group derived from benzene, naphthalene,anthracene, pyrene, acenaphthene, acenaphthylene, azulene, fluorene orthe like; or a mono- or divalent aromatic heterocyclic group derivedfrom dibenzofuran, carbazole, indole, thiophene, furan, pyrrole,pyrazole, acridine, xanthene or the like. Such aromatic hydrocarbyl andheterocyclic groups may or may not have a substituent, and suchsubstituent may be selected from those mentioned above as thesubstituents which may be possessed by said alkyl, aralkyl and arylgroups. Most preferably, A is an N-ethylcarbzolyl group orN,N-dialkylaminophenyl group.

In the general formula (I), n represents the number of 1 when A is amonovalent group and the number of 2 when A is a divalent group.

The hydrazone compound represented by the general formula (I) can beeasily produced by a known method. For example, such compound can beobtained by reacting a substituted hydrazine represented by thefollowing general formula (II): ##STR4## wherein R¹ and R² represent thesame groups as defined in the aforeshown general formula (I)) or itsmineral acid salts with an aldehyde represented by the general formula(III): ##STR5## (wherein n and A are as defined in the general formula(I)) in a slvent in a usual way. An alcohol such as methanol or ethanol,or acetic acid is favorably used as the solvent in this reaction, but itis also possible to use other types of solvent such as tetrahydrofuraneither singly or in admixture.

Listed hereinbelow are the typical examples of the hydrazone compoundsthat can be produced in the manner described above. (In the followingformulae, "Ph" represents phenyl group). ##STR6##

The electrophotographic plate according to this invention has aphotosensitive layer having an organic photoconductor layer containingat least one hydrazone compound represented by the above-shown generalformula (I).

The hydrazone compounds represented by the general formula (I) have veryexcellent properties as organic photoconductor, and particularly whenused as a charge transporting material, they can provide aphotosensitive plate with high sensitivity and excellent durability.

Various types of photosensitive layer are known and used inelectrophotographic plates, and any of such known types ofphotosensitive layer can be employed for the electrophotographic plateof this invention. Examples of such photosensitive layers usable in thisinvention include the following: a photosensitive layer composed of anorganic photoconductor layer formed by adding to a binder said hydrazonecompound and, if need be, a dye which serves as a sensitizer or anelectron acceptor which forms a charge transfer complex with saidhydrazone compound; a photosensitive layer composed of an organicphotoconductor layer formed by adding to a binder a photoconductivematerial which, when absorbing light, generates a charge carrier atextremely high efficiency and said hydrazone compound; or aphotosensitive layer consisting of a double-layer composed of an organicphotoconductor layer (functioning as a charge transporting layer) formedfrom said hydrazone compound and a binder and a charge generating layerformed from a photoconductive material which generates a charge carrierat very high efficiency upon absorbing light, or from saidphotoconductive material and a binder.

In the present invention, when an organic photoconductor layercontaining a hydrazone compound represented by the general formula (I)is used as the charge transporting layer of the double layeredphotosensitive lyaer formed from said charge transporting layer and acharge generating layer, there can be obtained a high-durability,photosensitive plate which is high in sensitivity and small in residualpotential and which, when used repeatedly, suffers little variation ofthe surface potential and is minimized in reduction of sensitivity andaccumulation of residual potential.

For the production of the electrophotographic plate according to thisinvention, first a hydrazone compound represented by the general formula(I) is dissolved in a suitable solvent together with a binder in a usualway to obtain a coating solution and, if need be, this solution isfurther comprised of a photoconductive material which generates a chargecarrier at extremely high efficiency upon absorbing light, a dye servingas a sensitizer, an electron acceptor which forms a charge transfercomplex with said hydrazone compound, a plasticizer, a pigment and otheradditives, and the thus prepared solution is applied on a conductivesubstrate and then dried to form on said substrate an organicphotoconductor layer with a thickness of usually several μm to severaltens of μm. In the case of the double-layered photosensitive layerformed from a charge generating layer and a charge transporting layer(that is, organic photoconductor layer), said solution is applied onsaid charge generating layer or the charge generating layer is formed onthe charge transporting layer which is formed by applying said solution.

The solvent used for the preparation of said coating solution may beselected from solvents capable of dissolving said hydrazone compoundssuch as: ethers such as tetrahydrofuran, 1,4-dioxane, etc.; ketones suchas methyl ethyl ketone, cyclohexanone, etc.; aromatic hydrocarbons suchas toluene, xylene, etc.; dipolar aprotic solvents such asN,N-dimethylformamide, acetonitrile, N-methylpyrrolidone, dimethylsulfoxide, etc.; esters such as ethyl acetate, methyl formate, methylcellosolve acetate, etc.; chlorinated hydrocarbons such asdichloroethane, chloroform, etc. It is of course necessary that thesesolvents are capable of dissolving the binder used.

The binders usable in this invention include various kinds of polymersor resins compatible with said hydrazone compounds such as: polymers andcopolymers of the vinyl compounds such as styrene, vinyl acetate, vinylchloride, acrylic acid esters, methacrylic acid esters, butadiene, etc.;polyvinyl acetals, polycarbonates, polyesters, polysulfones,polyphenylene oxides, polyurethanes, cellulose esters, cellulose ethers,phenoxy resins, silicone resins, epoxy resins, etc. Such binder isusually used in an amount 0.5 to 30 times, preferably 1 to 10 times byweight the amount of the hydrazone compound used.

The charge-generating photoconductor material, dye and electronacceptor, which are added, at need, to said photosensitive layer, may beof the known types.

The photoconductive material which generates a charge carrier atextremely high efficiency upon light absorption may be selected from:inorganic photoconductive materials such as selenium, selenium alloyssuch as selenium-tellurium alloy or selenium-arsenic alloy, and cadmiumsulfide; and organic photoconductive materials such as phthalocyaninepigments such as copper phthalocyanine, perione pigments, thioindigopigments, quinacridone pigments, perylene pigments, anthraquinonepigments, azo pigments, bisazo pigments, and cyanine pigments, etc. Mostpreferred among these photoconductive compounds are selenium,selenium-tellurium alloy, selenium-arsenic alloy, phthalocyaninepigments such as copper phthalocyanine, perylene pigments and bisazopigments. Examples of the perylene pigments are: ##STR7## Most preferredamong these bisazo pigments are bisazo compounds prepared by using a3-hydroxy-2-naphthamide derivative or a 4-hydroxy-1,8-naphthalimidederivative as coupler.

The dye used in this invention may be, for example, triphenylmethanedyes such as methyl violet, brilliant green, crystal violet, etc.;thiazine dyes such as methylene blue etc.; quinone dyes such asquinizarin etc.; cyanine dyes; pyrylium salts; thiapyrylium salts;benzopyrylium salts; etc.

Examples of the electron acceptors which form a charge transfer complexwith the hydrazone compound in this invention are quinones such aschloranil, 2,3-dichloro-1,4-naphthoquinone, 2-methylanthraquinone,1-nitroanthraquinone, 1-chloro-5-nitroanthraquinone,2-chloroanthraquinone, phenanthrenequinone, etc.; aldehydes such as4-nitrobenzaldehyde, etc.; ketones such as 9-benzoylanthracene,indandione, 3,5-dinitrobenzophenone, 2,4,7-trinitrofluorenone,2,4,5,7-tetranitrofluorenone, 3,3',5,5'-tetranitrobenzophenone, etc.;acid anhydrides such as phthalic anhydride, 4-chloronaphthalicanhydride, etc.; cyano compounds such as terephthalalmalononitrile,4-nitrobenzalmalononitrile, etc.; phthalides such as 3-benzalphthalide,3-(α-cyano-p-nitrobenzal)phthalide,3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide, etc.

Further, the photosensitive layer of the electrophotographic plateaccording to this invention may contain a known type of plasticizer forimproving the film-forming properties, flexibility and mechanicalstrength. The plasticizer to be added in said coating solution for saidpurpose is, for example, phthalic acid esters, phosphoric acid esters,epoxy compounds, chlorinated paraffins, chlorinated fatty acid esters,aromatic compounds such as methylnaphthalene, etc. In the case of usingthe hydrazone compound as a charge transporting material in the chargetransporting layer, the coating solution may be of the above-saidcomposition, but the charge-generating photoconductive material, dye andelectron acceptor may be excluded or they may be added in smallerquantities. The charge-generating layer used in this case may be a thinlayer (vacuum evaporation layer) obtained by vacuum-evaporating saidcharge-generating photoconductive material and, if necessary, a dye andan electron acceptor, or a thin layer (aggregate layer of thephotoconductive material particles) obtained by applying and drying acoating solution prepared by dissolving or dispersing saidcharge-generating photoconductive material in a solvent, or a thin layer(dispersion layer of the photoconductive material particles) obtained byapplying and drying a coating solution prepared by dispersing saidcharge-generating photoconductive material in a solvent together with abinder and/or other organic photoconductive material.

Needless to say, the thus obtained sensitive plate of this invention mayhave an auxiliary layer such as an adhesive layer, intermediate layer ortransparent insulating layer as in the commercially availableelectrophotographic sensitive plates. The conductive substrate on whichthe photosensitive layer is formed may be of any known type which iscommonly used for the electrophotographic plates. To cite some examples,such substrate may be a drum or sheet of a metal such as aluminum,copper, etc., or a laminate of such metal foils, or a metallized sheetthereof. It is also possible to use a plastic film, paper sheet or thelike which has conductive surface obtained by applying a conductivematerial such as metal powder, carbon black, copper iodide,high-molecular electrolyte or such with a suitable binder.

While the electrophotographic plate according to this invention has beendescribed in detail, it should be also noted that the hydrazone compoundemployed for the production of such electrophotographic plate has highcharge carrier transporting efficiency and can be therefore used incombination with various types of charge carrier generating materials.It also allows obtainment of a sensitive plate with excellent printingdurability because of its good compatibility with resins, particularlywith polycarbonates, polyesters, acrylic and methacrylic resins.Further, the hydrazone compound contained in the photosensitive layerhas excellent transparency and allows light transmission even in adouble layer type comprising a charge carrier transporting layer on acharge carrier generating layer, making it possible to obtain ahigh-sensitivity plate.

Thus, the plate provided according to this invention is very high insensitivity, small in residual potential that may cause backgrounddeposition of toner, minimized in accumulation of residual potentialfrom repeated uses and variations in surface potential and sensitivity,and also excellent in durability.

The invention is now described in further detail by way of the followingexamples, but it will be understood that the scope of this invention isnot limited to these examples but covers other forms of embodimentswithout departing from the gist of the invention. All the "parts"appearing in the following Examples are by weight unless otherwisespecified.

EXAMPLE 1

1,1-diphenylhydrazine and N-ethylcarbazole-3-carbaldehyde were reactedin ethanol at room temperature to obtain N-ethylcarbazole-3-carbaldehydediphenylhydrazone with melting point of 160.2°-160.5° C., and 60 partsof this hydrazone compound and 100 parts of a polyester (Vylon 200 byToyobo Co., Ltd.) were dissolved in 450 parts of tetrahydrofuran toprepare a coating solution. Then selenium was vacuum evaporated on a 10μm thick aluminum foil laminated on a 75 μm thick polyester film to forma charge generating layer with thickness of approximately 0.3 μm, and tothis layer was applied the above-said coating solution by a filmapplicator and dried to form a 20 μm thick charge transporting layer. Inthis way, there was obtained a double-layer type electrophotographicplate.

The sensitivity, or half-decay exposure intensity (E_(1/2)), of thisplate was 6 lux.sec. The half-decay exposure intensity was determined byfirst charging the plate by -5.5 KV corona discharge in a dark place,then exposing it to incandescent light and measuring the exposureintensity required till the surface potential decayed to one half of theinitial surface potential. The exposure intensity (E_(1/5)) requiredtill the surface potential decayed down to 1/5 of the initial surfacepotential was 13 lux.sec.

EXAMPLE 2

An electrophotographic plate was produced by following the sameprocedure as Example 1 except for use of a vacuum evaporation film ofselenium-tellurium alloy (15% tellurium content) instead of the seleniumevaporation film for the charge generating layer.

E_(1/2) and E_(1/5) of this plate were 1.6 lux.sec and 3.6 lux.sec,respectively.

EXAMPLE 3

Aluminum was deposited on a 100 μm thick polyester film by vacuumevaporation to the thickness of 600 A, and then phthalocyanine wasfurther deposited thereon to the thickness of approximately 0.2 μm toform a charge generating layer. Then a coating solution prepared bydissolving 60 parts of N,N-diethylamino-p-benzaldehyde diphenylhydrazone(melting point: 93.0°-93.5° C.) and 100 parts of polyester (Vylon 200)in 450 parts of tetrahydrofuran was applied on said charge generatinglayer by a film applicator and dried to form a 20 μm thick chargetransporting layer.

The sensitivity of the thus obtained plate was E_(1/2) =3 lux.sec andE_(1/5) =5.7 lux.sec.

EXAMPLES 4-8

A bisazo compound having the following structural formula: ##STR8## wasdispersed in tetrahydrofuran and finely pulverized by a sand grinder,and the dispersion concentration was adjusted such that the bisazocompound: tetrahydrofuran ratio would become 1:90 by parts. Thisdispersion was applied on the aluminum foil of the same type of laminatefilm as used in Example 1 by a film applicator such that the weightafter drying would become 0.1 g/m² and then dried to form a chargegenerating layer. Then a solution prepared by dissolving 70 parts of ahydrazone compound shown in Table 1 and 100 parts of a polycarbonate(NOVAREX 7025 A by Mitsubishi Chemical Industries Ltd.) in 850 parts oftetrahydrofuran was applied on said charge generating layer by a filmapplicator such that the film thickness after drying would become 15 μmand then dried to form a charge transporting layer. There were obtainedin this way the electrophotographic plates having a double-layeredphotosensitive layer.

The sensitivity (E_(1/2)) to incandescent light of the thus obtainedplates is shown in Table 1. Charging was effected by means of -5 KVcorona discharge. In the following table, Ph represents phenyl group.

                                      TABLE 1                                     __________________________________________________________________________                               melting point                                                                 of the hydrazone                                   Example                                                                            hydrazone compound    compound E.sub.1/2 (lux . sec)                     __________________________________________________________________________          ##STR9##             124.0- 124.5° C.                                                                21                                        5                                                                                   ##STR10##            156.0- 156.5° C.                                                                6.2                                       6                                                                                   ##STR11##            196.0- 197.5° C.                                                                8.7                                       7                                                                                   ##STR12##            241.0- 241.5° C.                                                                4.0                                       8                                                                                   ##STR13##            122.5- 123.0° C.                                                                7.5                                       __________________________________________________________________________

EXAMPLE 9

1 part of a bisazo compound having the following structural formula:##STR14## and 1 part of a polyester (Vylon 200 by Toyobo Co., Ltd.) wereadded to 90 parts of tetrahydrofuran, and the mixture was subjected to adispersion treatment by a sand grinder after the manner of Example 4 andapplied on the aluminum surface of an aluminum foil laminated polyesterfilm such that a deposit of 0.2 g/m² would be provided after drying,thereby forming a charge generating layer. Then a coating solutionprepared by dissolving 70 parts of a hydrazone compound (same as used inExample 1), 3 parts of3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide and 100 parts ofthe above-said polyester (Vylon 200) in a mixed solvent of 700 parts oftoluene and 160 parts of methyl ethyl ketone was applied on said chargegenerating layer such that a film thickness of 15 μm would be providedafter drying, thereby forming a charge transporting layer. There wasthus obtained an electrophotographic plate having a double-layeredphotosensitive layer.

This plate was subjected to a durability test by an electrostatic paperanalyzer (Model SP-428 by Kawaguchi Denki Seisakujo). While rotating theturntable carring the plate sample at the rate of approximately 1,000r.p.m. according to the dynamic method, the sample plate was subjectedto -6.6 KV corona discharge for 3 seconds and then exposed toincandescent light with illuminance of 330 lux for 5 seconds, and thiscycle was repeated while measuring the sensitivity upon everypredetermined number of revolutions according to the static method. Thesensitivity before the repetition test was E_(1/2) =3.0 lux.sec andE_(1/5) =5.5 lux.sec under the conditions of -6 KV corona discharge and5 lux incandescent light exposure, and the residual potential expressedin terms of surface potential after exposure of 50 lux.sec was -20 V.After 2,000 times of repetition of said charging and exposure, E_(1/2)was 3.4 lux.sec, E_(1/5) was 6.2 lux.sec and residual potential was - 10V. Thus, the variations caused by such 2,000 times of repetition werevery limited. The maximum surface potential before exposure was 1,480 Vbefore the repetition test and 1,570 V after 2,000 times of repetition.

This plate was set in an electrophotographic copying machine (U-Bix-800by Konishiroku Photo Ind. Co., Ltd.) and used for copying an original.There was obtained a clear image with no fogging.

EXAMPLE 10

3 parts of β-type copper phthalocyanine was added to 900 parts oftetrahydrofuran and, after ultrasonic dispersion thereof, 100 parts of apolycarbonate (NOVAREX 7025 A by Mitsubishi Chemical Industries Ltd.)and 60 parts of a hydrazone compound used in Example 1 were added anddissolved in said dispersion to prepare a coating solution, and thissolution was applied on the aluminum surface of an aluminum foillaminated polyester film by a film applicator such that the filmthickness after drying would become 15 μm and then dried thereby forminga photosensitive layer to obtain an electrophotographic plate. Thisplate was charged by +6 KV corona discharge in a dark place and then itssensitivity was measured. E_(1/2) was 8 lux.sec.

EXAMPLE 11

100 parts of a hydrazone compound same as used in Example 1, 100 partsof a polyester (Vylon 200) and 10 parts of bromanil were dissolved in450 parts of tetrahydrofuran, and this solution was applied on thealuminum surface of an aluminum foil laminated film by a film applicatorsuch that a 15 μm film thickness would be provided after drying, therebyforming a photosensitive layer to obtain an electrophotographic plate.This plate was charged by +6 KV corona discharge in a dark place and itssensitivity was measured, obtaining E_(1/2) =223 lux.sec.

EXAMPLE 12

Aluminum was deposited on a 75 μm thick polyester film by vacuumevaporation to the thickness of 600 A and then a 1 μm thick intermediatelayer composed of a polyamide (CM-4000 by Toray Industries Inc.) wasformed thereon, followed by further provision thereon of a chargegenerating layer same as provided in Example 9. Then a coating solutionprepared by dissolving 80 parts of a hydrazone compound same as used inExample 1, 0.8 part of3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide, 4 parts of1,1-dicyano-2-(9'-anthryl) ethylene and 100 parts of a methacrylic resin(DIANAL BR-85 by Mitsubishi Rayon Co., Ltd.) in a mixed solvent of 700parts of toluene and 160 parts of methyl ethyl ketone was applied onsaid charge generating layer such that a 25 μm film thickness would beprovided after drying, thereby forming a double-layered photosensitivelayer to obtain an electrophotographic plate.

This plate was wound on an aluminum drum with outer diameter of 60 mmand used as the sensitive plate for a copying machine (Type EG-101 byMinolta Camera Co., Ltd.). After 100,000 times of repetition of chargingand exposure, there could still be obtained a clear, fog-free imagelittle different from the initial image, indicating very excellentdurability of this plate.

EXAMPLE 13

A charge generating layer same as used in Example 4 was provided on anintermediate layer formed in the same way as Example 12, and then acoating solution prepared by dissolving 60 parts of a hydrazone compoundsame as used in Example 1, 1.2 parts of3-(α-cyano-p-nitrobenzal)-4,5,6,7-tetrachlorophthalide and 100 parts ofa polyester (Vylon 200) in a mixed solvent of 700 parts of toluene and160 parts of methyl ethyl ketone was applied on said charge generatinglayer such that a 28 μm film thickness would be provided after drying,thereby forming a charge transporting layer to obtain anelectrophotographic plate having a double-layered photosensitive layer.

This plate was subjected to a repetition test by an electrostatic paperanalyzer same as used in Example 9. By using the dynamic method, theplate was subjected to 2-second charging at -6.5 KV, 0.5-second standingin a dark place and 1-second exposure to 350 lux incandescent light andthis cycle was repeated while measuring the sensitivity upon everypredetermined number of revolutions according to the static method. Theresults are shown in Table 2. The measurement according to the staticmethod was made under the conditions of 6 KV corona discharging voltageand 5 lux incandescent light illuminance. In the table, Vm indicates themaximum surface potential before exposure and Vr indicates the residualpotential after 10-second exposure. Sensitivity was expressed in termsof exposure intensity required till the surface potential dropped from1,400 V to 700 V. It will be noted that the variations of Vm, Vr andsensitivity are very small.

                  TABLE 2                                                         ______________________________________                                        number of                                                                     revolutions                                                                            Vm (V)    Vr (V)    Sensitivity (lux . sec)                          ______________________________________                                        0        -1870     -10       4.5                                              1,000    -1800     - 5       4.0                                              2,000    -1840     -10       4.5                                              5,000    -1820     - 5       4.5                                              7,000    -1840     -15       4.6                                              10,000   -1800     -10       4.5                                              ______________________________________                                    

What is claimed is:
 1. An electrophotographic plate comprising aconductive substrate and a photosensitive layer coated thereon; whereinsaid photosensitive layer comprises an organic photoconductor layer; andwherein said organic photoconductor layer comprises a hydrazone compoundrepresented by the general formula (I): ##STR15## wherein R¹ and R² areindependently selected from the group consisting of substituted orunsubstituted alkyl, substituted or unsubstituted aralkyl, andsubstituted or unsubstituted aryl, n is a number of 1 or 2, and A is anunsubstituted or substituted aromatic heterocyclic group, and a binder.2. The electrophotographic plate, according to claim 1, wherein at leastone of R¹ and R² in the general formula (I) is an aryl group.
 3. Theelectrophotographic plate, according to claim 1, wherein A in thegeneral formula (I) is N-ethylcarbazolyl group.
 4. Theelectrophotographic plate, according to any of claims 1 to 3, whereinthe organic photoconductor layer contains a dye.
 5. Theelectrophotographic plate, according to any of claims 1 to 3, whereinthe organic photoconductor layer contains an electron acceptor whichforms a charge transfer complex with said hydrazone compound.
 6. Theelectrophotographic plate, according to any of claims 1 to 3, whereinthe organic photoconductor layer contains a photoconductive materialwith high charge generating efficiency selected from the groupconsisting of selenium, selenium alloys, cadmium sulfide, phthalocyaninepigments, perinone pigments, thioindigo pigments, quinacridone pigments,perylene pigments, anthraquinone pigments, azo pigments, bisazo pigmentsand cyanine pigments.
 7. The electrophotographic plate, according to anyof claims 1 to 3, wherein said photosensitive layer comprises adouble-layer composed of said organic photoconductor layer functioningas a charge transporting layer and a charge generating layer containinga photoconductive material with high charge generating efficiencyselected from the group consisting of selenium, selenium alloys, cadmiumsulfide, phthalocyanine pigments, perinone pigments, thioindigopigments, quinacridone pigments, perylene pigments, anthraquinonepigments, azo pigments, bisazo pigments and cyanine pigments.
 8. Theelectrophotographic plate, according to claim 7, wherein the chargegenerating layer is formed from an aggregate of the particles of saidphotoconductive material with high charge generating efficiency.
 9. Theelectrophotographic plate, according to claim 7, wherein the chargegenerating layer is a dispersion of the particles of saidphotoconductive material with high charge generating efficiency in abinder.
 10. The electrophotographic plate, according to claim 8, whereinsaid photoconductive material with high charge generating efficiency isat least one material selected from the group consisting of selenium,selenium alloys, cadmium sulfide, phthalocyanine pigment, perinonepigment, perylene pigment, bisazo pigment and cyanine pigment.
 11. Theelectrophotographic plate, according to claim 9, wherein saidphotoconductive material with high charge generating efficiency is abisazo pigment.
 12. The electrophotographic plate, according to claim 7,wherein said charge generating layer is a vacuum evaporation layer ofsaid photoconductive material with high charge generating efficiency.13. The electrophotographic plate, according to claim 12, wherein saidphotoconductive material with high charge generating efficiency is atleast one of the group consisting of selenium, selenium alloys,phthalocyanine pigment and perylene pigment.
 14. The electrophotographicplate, according to claim 9, wherein said photoconductive material is atleast one material selected from the group consisting of selenium,selenium alloys, cadmium sulfide, phthalocyanine pigment, perinonepigment, perylene pigment, bisazo pigment and cyanine pigment.
 15. Theelectrophotographic plate, according to claim 8, wherein saidphotoconductive material is a bisazo pigment.